7,011 research outputs found
Cash Versus In-Kind Transfers: Comparative Differences and Individual Best Practices to Benefit Recipient Communities
This research paper seeks to compare cash and in-kind transfers in the context of foreign poverty aid to determine which transfer style is most beneficial and to evaluate long-term best practices of each kind to more positively benefit the recipient communities. It does this by comparing arguments for and against each transfer model. The first argument discusses the differences in distribution costs between the two models. The second compares the cash transfer’s strong concept of choice with in-kind transfer’s typical style of controlled consumption of goods. The second argument discusses the timing and impact of targeting communities in connection to each transfer style. Finally, the last argument discusses the contrasting macroeconomic impact each style has on local markets. Cash transfers are predetermined cash donations given either as a lump sum or in periodic transfers. Conversely, in-kind transfers are direct transfers of physical goods distributed to households. This paper maintains that both transfer styles have the capability of being beneficial if they are planned and executed with extensive knowledge of the unique local community, its needs, the economic and social effects of each transfer style, and a purposeful design aimed at long-term growth and empowerment of communities
Robustness of 3D Deep Learning in an Adversarial Setting
Understanding the spatial arrangement and nature of real-world objects is of
paramount importance to many complex engineering tasks, including autonomous
navigation. Deep learning has revolutionized state-of-the-art performance for
tasks in 3D environments; however, relatively little is known about the
robustness of these approaches in an adversarial setting. The lack of
comprehensive analysis makes it difficult to justify deployment of 3D deep
learning models in real-world, safety-critical applications. In this work, we
develop an algorithm for analysis of pointwise robustness of neural networks
that operate on 3D data. We show that current approaches presented for
understanding the resilience of state-of-the-art models vastly overestimate
their robustness. We then use our algorithm to evaluate an array of
state-of-the-art models in order to demonstrate their vulnerability to
occlusion attacks. We show that, in the worst case, these networks can be
reduced to 0% classification accuracy after the occlusion of at most 6.5% of
the occupied input space.Comment: 10 pages, 8 figures, 1 tabl
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Design of Experiments Approach for Statistical Classification of Stereolithography Manufacturing Build Parameters: Effects of Build Orientation on Mechanical Properties for ASTM D-638 Type I Tensile Test Specimens of DSM Somos® 11120 Resin
A statistical design of experiments (DOE) approach was used to determine if specific build
orientation parameters impacted mechanical strength of fabricated parts. A single platform (10-
inch by 10 inch cross-section) on the 3D Systems Viper si2 machine was designed to hold 18,
ASTM D-638 Type I samples built in six different orientations (called Location) with three
samples built for each location. The DOE tested four factors: Location, Position, Axis, and
Layout. Each sample within a Location was labeled as Positions 1, 2, or 3 depending on the
distance from the center of the platform with Position 1 being the closest to the center. Samples
were fabricated parallel with the x-axis, y-axis, or 45o
to both axes (called Axis 1, 2, and 3,
respectively) and were fabricated either flat or on an edge relative to the x-y plane (called Layout
1 and 2, respectively). The results from the statistical analyses showed that Axis, Location, and
Position had no significant effect on UTS or E. However, Layout (or whether a sample was built
flat or on an edge) was shown to have a statistically significant effect on UTS and E (at a 95%
level of confidence). This result was not expected since a comparison of the average UTS for
each Layout showed only a 1.2% difference (6966 psi versus 7050 psi for samples built flat and
on an edge, respectively). Because of the small differences in means for UTS, the statistical
differences between Layout most likely would not have been identified without performing the
DOE. Furthermore, Layout was the only factor that tested different orientations of build layers
(or layer-to-layer interfaces) with respect to the sample part, and thus, it appears that the
orientation of the build layer with respect to the fabricated part has a significant effect on the
resulting mechanical properties. This study represents one of many to follow that is using
statistical analyses to identify and classify important fabrication parameters on mechanical
properties for layer manufactured parts. Although stereolithography is the focus of this work, the
techniques developed here can be applied to any layered manufacturing technology.Mechanical Engineerin
Clustering of Local Group distances: publication bias or correlated measurements? I. The Large Magellanic Cloud
The distance to the Large Magellanic Cloud (LMC) represents a key local rung
of the extragalactic distance ladder. Yet, the galaxy's distance modulus has
long been an issue of contention, in particular in view of claims that most
newly determined distance moduli cluster tightly - and with a small spread -
around the "canonical" distance modulus, (m-M)_0 = 18.50 mag. We compiled 233
separate LMC distance determinations published between 1990 and 2013. Our
analysis of the individual distance moduli, as well as of their two-year means
and standard deviations resulting from this largest data set of LMC distance
moduli available to date, focuses specifically on Cepheid and RR Lyrae
variable-star tracer populations, as well as on distance estimates based on
features in the observational Hertzsprung-Russell diagram. We conclude that
strong publication bias is unlikely to have been the main driver of the
majority of published LMC distance moduli. However, for a given distance
tracer, the body of publications leading to the tightly clustered distances is
based on highly non-independent tracer samples and analysis methods, hence
leading to significant correlations among the LMC distances reported in
subsequent articles. Based on a careful, weighted combination, in a statistical
sense, of the main stellar population tracers, we recommend that a slightly
adjusted canonical distance modulus of (m-M)_0 = 18.49 +- 0.09 mag be used for
all practical purposes that require a general distance scale without the need
for accuracies of better than a few percent.Comment: 35 pages (AASTeX preprint format), 5 postscript figures; AJ, in
press. For full database of LMC distance moduli, see
http://astro-expat.info/Data/pubbias.htm
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Hydrogels in Stereolithography
The use of stereolithography (SL) for fabricating complex three-dimensional (3D) tissue
engineered scaffolds of aqueous poly(ethylene glycol) (PEG) hydrogel solutions is described.
The primary polymer used in the study was PEG-dimethacrylate (PEG-dma) with an average
molecular weight (MW) of 1000 in distilled water with the photoinitiator Irgacure 2959 (I-2959).
Successful layered manufacturing (LM) with embedded channel architecture required
investigation of the photopolymerization characteristics of the PEG solution (measured as
hydrogel thickness or cure depth) as a function of photoinitiator concentration and laser energy
dosage for a specific photoinitiator type and polymer concentration in solution. Hydrogel
thickness was a strong function of PI concentration and energy dosage. Curves of hydrogel
thickness were utilized to successfully plan, perform, and demonstrate layered manufacturing of
highly complex hydrogel scaffold structures, including structures with internal channels of
various orientations. Successful fabrication of 3D, multi-layered bioactive PEG scaffolds
containing cells was accomplished using a slightly modified commercial SL system (with 325
nm wavelength laser) and procedure. Human dermal fibroblast (HDF) cells were encapsulated in
PEG hydrogels using small concentrations (~ 5 mg/ml) of acryloyl-PEG-RGDS (MW 3400)
added to the photopolymerizable PEG solution to promote cell attachment. HDF cells were
combined with the PEG solution, photocrosslinked using SL, and successfully shown to survive
the fabrication process. The combined use of SL and photocrosslinkable biomaterials such as
PEG makes it possible to fabricate complex 3D scaffolds that provide site-specific and tailored
mechanical properties (i.e., multiple polymer materials) with a polymer matrix that allows
transport of nutrients and waste at the macroscale and facilitates cellular processes at the
microscale through precisely placed bioactive agents.Mechanical Engineerin
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Effect of Surface Preparation Methods on Mechanical Properties of 3D Structures Fabricated by Stereolithography and 3D Printing for Electroless Ni Plating
Stereolithography (SL) and 3D Printing (3DP) are useful technologies for
three-dimensional prototyping applications, providing highly accurate and detailed part
geometries with high quality surface finishes. It is desired to improve the materials
performance of the existing photocurable SL and 3DP resins for rapid tooling and other
functional applications by applying a nickel (Ni) coating. In this work, surface
preparation methods for electroless plating of commercial photopolymer resins such as
NanoFormTM15120 (NanoForm) and Objet FullCure®840 (Veroblue) were explored in
order to enhance the structural integrity of RP components. This study examined
different surface preparation methods (chemical etching) and their effect on the surface
morphology and mechanical strength of the polymers. It was observed that surface
preparation of the resins significantly affected the mechanical properties and Ni plating of
the substrate polymers. This is a critical step, since the Ni film takes on the surface
structure of the substrate.Mechanical Engineerin
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Multi-Material Stereolithography: Spatially-Controlled Bioactive Poly(Ethylene Glycol) Scaffolds for Tissue Engineering
Challenges remain in tissue engineering to control the spatial and temporal mechanical and
biochemical architectures of scaffolds. Unique capabilities of stereolithography (SL) for
fabricating multi-material spatially-controlled bioactive scaffolds were explored in this work. To
accomplish multi-material builds with implantable materials, a new mini-vat setup was designed,
constructed and placed on top of the existing build platform to allow for accurate and selfaligning X-Y registration during fabrication. Precise quantities of photocrosslinkable solution
were added to and removed from the mini-vat using micro-pipettes. The mini-vat setup allowed
the part to be easily removed and rinsed and different photocrosslinkable solutions could be
easily removed and added to the vat to aid in multi-material fabrication. Two photocrosslinkable
hydrogel biopolymers, poly(ethylene glycol dimethacrylate) (PEG-dma, molecular wt 1,000) and
poly(ethylene glycol)-diacrylate (PEG-da, molecular wt 3,400), were used as the primary
scaffold materials, and controlled concentrations of fluorescently labeled dextran or bioactive
PEG were prescribed and fabricated in different regions of the scaffold using SL. The
equilibrium swelling behavior of the two biopolymers after SL fabrication was determined and
used to design constructs with the specified dimensions at the swollen state. Two methods were
used to measure the spatial gradients enabled by this process with multi-material spatial control
successfully demonstrated down to 500-µm. First, the presence of the fluorescent component in
specific regions of the scaffold was analyzed with fluorescent microscopy. Second, human
dermal fibroblast cells were seeded on top of the fabricated scaffolds with selective bioactivity,
and phase contrast microscopy images were used to show specific localization of cells in the
regions patterned with bioactive PEG. The use of multi-material SL and the relative ease of
conjugating different bioactive ligands or growth factors to PEG allows for the fabrication of
tailored three-dimensional constructs with specified spatially-controlled bioactivity.Mechanical Engineerin
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